lect 19

Question 1

what are the steps in water treatment?

Answer 1

A- primary settling
B- aeration
C- removal of excess hardness, Fe and Mn
D- coagulation
E- disinfection

Question 2

what is primary settling (treatment steps)?

Answer 2

-allow larger particles to settle out in a holding basin
-pH is controlled by adding lime

Question 3

what is aeration (treatment steps)?

Answer 3

-remove volatile substances
-remove easily oxidizable substances

ferrous iron (Fe2+) can be removed by precipitation to ferric iron (Fe(OH)3)
-colloidal suspensions harder to remove
-homeowners can remove Fe(II) using oxidizing filters

Question 4

what is the removal of excess hardness (treatment steps)?

Answer 4

Question 5

what is coagulation (treatment steps)

Answer 5

Question 6

what is alum?

Answer 6

Question 7

what is disinfection (treatment steps)?

Answer 7

-water is made drinkable by killing pathogens
-one of the last steps in drinking water treatment

methods:
1. chlorine
2. chlorine dioxide
3. ozone
4. UV radiation

-important: need “residual activity” in water to prevent recontamination

Question 8

what is chlorine equilibria in water?

Answer 8

Question 9

what species of chlorine is effective at killing bacteria?

Answer 9

HOCl is a neutral molecule and can readily diffuse into cell membranes of bacterias

Question 10

what are trihalomethanes?

Answer 10

Question 11

what is chlorine demand?

Answer 11

the amount of chlorine that is required to satisfy all the impurities (i.e. the amount of chlorine needed before free chlorine can be produced)
-once the chlorine demand has been met, breakpoint chlorination (the addition of chlorine to water until the chlorine demand has been satisfied) has occurred

additional chlorine added beyond the “breakpoint” will result in a free chlorine residual proportional to the amount of chlorine added. Depending on the chemical species, free forms are: HOCL and ClO-

Question 12

how do we increase chlorine residual? what are the advantages and the problems?

Answer 12

Question 13

what is ammonia removal via denitrification?

Answer 13

Question 14

Question 15

what is chlorine dioxide?

Answer 15

Question 16

what are the disadvantages of chlorine dioxide?

Answer 16

Question 17

what is ozone? what are the disadvantages?

Answer 17

Question 18

what is the ozone generation and water treatment graph?

Answer 18

Question 19

what is UV radiation? what are the advantages?

Answer 19

Question 20

what are the disadvantages of UV radiation?

Answer 20

Question 21

what are inorganic contaminants in drinking water?

Answer 21

-lead
-cadmium and mercury (cumulative poisons)
-aluminum
-sodium
-organotin compounds

Question 22

what is lead contamination in drinking water?

Answer 22

Question 23

what is cadmium contamination?

Answer 23

Question 24

what is mercury contamination?

Answer 24

Question 25

what is grassy narrows?

Answer 25

a case of mercury poisoning

Question 26

what is aluminum contamination?

Answer 26

Question 27

what is sodium contamination?

Answer 27

Question 28

what is aluminium acetylsalicylate?

Answer 28

Question 29

what are organotin compounds?

Answer 29

Question 30

what are sources of organics in the drinking water supply? what are PCBs?

Answer 30

Question 31

how do we treat organics in drinking water?

Answer 31

-oxidation by secondary waste treatment methods (see lecture notes on sewage treatment) -adsorption on activated carbon (charcoal) filters -reverse osmosis: also used to desalinate water, expensive

Question 32

what are the two main sources of water sewage treatment?

Answer 32

-aqueous municipal wastes -other aqueous wastes from industry and agriculture

Question 33

why is sewage treatment necessary and what are the three steps?

Answer 33

Question 34

what is primary settling (sewage treatment)?

Answer 34

Question 35

what is secondary treatment (sewage treatment)?

Answer 35

Question 36

what is the trickling filter? what are the disadvantages?

Answer 36

-large cylindrical tank containing a bed of gravel and sand (the simplest way to reduce BOD) -provides a support for a colony of micro-organisms -micro-organisms degrade BOD in a controlled manner disadvantages: -can be poisoned by toxic industrial wastes -does not work well in colder climates

Question 37

what is the activated sludge process? what is done with effluent water?

Answer 37

Question 38

what are the graphs of secondary treatment? (sewage)

Answer 38

Question 39

what is sewage sludge? what are sludge disposal options?

Answer 39

Question 40

what are the problems with sludge?

Answer 40

persistent organics -resistant organo-chloride compounds (see chapter 7) inorganics -heavy metals from industrial sources-Cr, Cd, Pb, Hg, Ni, Ag, Zn, Cu -can be taken up by plants or leach from soil

Question 41

what is tertiary treatment?

Answer 41

Question 42

how to remove phosphates (TT):

Answer 42